Generally, a vehicle is provided with a passenger protecting system for protecting passengers in a collision of the vehicle. The passenger protecting system has, for example, an airbag device for deploying an airbag to protect the head portion or the like of the passenger, and/or a pre-tensioner device for taking up a slack of a seat belt of the vehicle.
The airbag device and the pre-tensioner device are controlled by a control unit such as an ECU. The ECU performs a determination of a vehicle collision based on signals from sensors mounted to the vehicle, and actuates the airbag device and the pre-tensioner device when the vehicle collision is determined.
It is desirable for the passenger protecting system to protect the passenger not only from a vehicle collision in the vehicle traveling direction (i.e., vehicle front-rear direction), but also from a side collision of the vehicle which causes a vehicle-width-direction impact on the vehicle. For example, as disclosed in JP-2-249740A, the airbag device for protecting the passenger from the side collision of the vehicle is provided with a side airbag, which can be deployed according to detection signals of a pressure sensor. The pressure sensor detects the variation of an inner pressure of the vehicle door.
As shown in FIG. 4, a pressure sensor 1 for detecting the side collision has a substantially hollow case 2 and a circuit assembly 3 which is fixedly housed in the case 2. The case 2 is provided with an air passage 22 for communicating the interior of the case 2 with the exterior. The pressure sensor 1 which is required to have a high watertightness performance is provided with a rubber packing 7 between the case 2 and a sensing unit 31 (for detecting pressure) of the circuit assembly 3. Thus, water is restricted from intruding upon the case 2 except the surface of the sensing unit 31, by the rubber packing 7 arranged between the circuit assembly 3 and the case 2. Therefore, a malfunction due to a wetting of a circuit board 30 is restricted.
However, because the pressure sensor 1 is provided with the rubber packing 7 for sealing, it is necessary for the circuit board 30, the pressure detecting unit 31 and the housing 2 of the pressure sensor 1 to be provided with high dimension accuracy. Therefore, the manufacture cost is increased.
Moreover, the pressure sensor 1 is constructed in such a manner that the case 2 and the pressure detecting unit 31 mounted to the circuit board 30 press against the rubber packing 7. That is, the stress pressing the rubber packing 7 is transferred to a coupling part between the circuit board 30 and the pressure detecting unit 31. Therefore, it is difficult to maintain the reliability of the sensing unit 31, the electrical connection portion and the circuit elements of the pressure sensor 1.
Furthermore, in order to improve the watertightness performance and restrict the malfunction due to stress concentration, the pressure sensor 1 is provided with a potting member 8 which is constructed by an injection of a potting material to support the circuit assembly 3 and the circuit board 30. Thus, the manufacture cost is further increased.